U.S. patent number 4,857,388 [Application Number 07/110,296] was granted by the patent office on 1989-08-15 for magnetic recording medium.
This patent grant is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Hiroshi Ogawa, Yasuo Tamai.
United States Patent |
4,857,388 |
Ogawa , et al. |
August 15, 1989 |
Magnetic recording medium
Abstract
A magnetic recording medium comprises a nonmagnetic support and
a magnetic recording layer provided on the support which comprises
two layers including a first magnetic recording layer and a second
magnetic recording layer. Each of the two magnetic recording layers
contains a ferromagnetic powder having a coercive force of not less
than 500 Oe dispersed therein. The first magnetic recording layer
is provided on the support has a Young's modulus of 500 to 1,000
kg/mm.sup.2 ; and the second magnetic recording layer provided on
the first magnetic recording layer has a Young's modulus of not
less than 1,300 kg/mm.sup.2 ; and the magnetic recording layers as
a whole show a Young's modulus of not less than 900
kg/mm.sup.2.
Inventors: |
Ogawa; Hiroshi (Kanagawa,
JP), Tamai; Yasuo (Kanagawa, JP) |
Assignee: |
Fuji Photo Film Co., Ltd.
(Kanagawa, JP)
|
Family
ID: |
17184471 |
Appl.
No.: |
07/110,296 |
Filed: |
October 20, 1987 |
Foreign Application Priority Data
|
|
|
|
|
Oct 20, 1986 [JP] |
|
|
61-248858 |
|
Current U.S.
Class: |
428/212; 428/900;
428/839.6; 427/131; 428/336; G9B/5.278 |
Current CPC
Class: |
G11B
5/716 (20130101); Y10S 428/90 (20130101); Y10T
428/24942 (20150115); Y10T 428/265 (20150115) |
Current International
Class: |
G11B
5/716 (20060101); G11B 005/70 () |
Field of
Search: |
;428/212,694,900,336
;427/131 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Thibodeau; Paul J.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
We claim:
1. A magnetic recording tape comprising a nonmagnetic support and a
magnetic recording layer provided on the support which comprises
two layers including a first magnetic recording layer and a second
magnetic recording layer, each of said first and second magnetic
recording layers comprising a binder and a ferromagnetic powder
having a coercive force of not less than 500 Oe dispersed therein,
wherein:
said first magnetic recording layer provided on the nonmagnetic
support has a Young's modulus in the longitudinal direction of 500
to 1,000 kg/mm.sup.2 ;
said second magnetic recording layer provided on the first magnetic
recording layer has a Young's modulus in the longitudinal direction
of not less than 1,300 kg/mm.sup.2 ; and
the magnetic recording layers as a whole show a Young's modulus in
the longitudinal direction of not less than 900 kg/mm.sup.2.
2. The magnetic recording tape as claimed in claim 1, wherein said
each of the binders of the first and second magnetic recording
layers contains a vinyl chloride copolymer and a polyurethane
resin.
3. The magnetic recording tape as claimed in claim 1, wherein the
total thickness of the first magnetic recording layer and the
second magnetic recording layer is in the range of 2 to 10
.mu.m.
4. The magnetic recording tape as claimed in claim 1, wherein the
thickness of the second magnetic recording layer is not larger than
2 .mu.m, and the thickness of the first magnetic recording layer is
larger than that of the second magnetic recording layer.
5. The magnetic recording tape as claimed in claim 1, wherein the
binder of the first magnetic recording layer contains a
polyurethane resin in an amount of not less than 60 wt.%.
6. The magnetic recording tape as claimed in claim 1, wherein the
binder of the first magnetic recording layer contains a vinyl
chloride copolymer and a polyurethane resin, the amount of the
polyurethane being not less than 60 wt.% of the total binder.
7. The magnetic recording tape as claimed in claim 1, wherein the
ferromagnetic powder of the first and second magnetic recording
layers are Co-containing .gamma.-magnetic powder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium which
is improved in electromagnetic conversion characteristics, running
property and running endurance.
2. Description of Prior Art
Magnetic recording media have been widely employed in recent years
as an audio tape, a video tape or a magnetic tape for a computer
system. The magnetic recording medium is desired to be excellent in
various properties such as electromagnetic conversion
characteristics, running property and running endurance.
For enhancing the electromagnetic conversion characteristics of the
medium, for example, a method of improving a coercive force (Hc) of
a ferromagnetic powder to be employed has been utilized, and
recently a ferromagnetic powder having a coercive force of not less
than 500 Oe is generally employed.
Further, a magnetic recording medium such as an audio tape or a
video tape has been broadly used in the form of a cassette encasing
the tape therein. In the case of such tape encased in a cassette
(i.e., cassette tape), a demand for longer time recording has
increased, and hence the tape is apt be made thinner. A magnetic
recording medium generally comprises a nonmagnetic support and a
magnetic recording layer provided on the support, so that it is
thought that the thickness of the magnetic recording layer is made
smaller for the purpose of making the magnetic recording medium as
a whole thinner. However, if the thickness of the magnetic
recording layer is made smaller, an adverse effect is given to the
electromagnetic conversion characteristics of the resulting medium.
Accordingly, the thickness of the nonmagnetic support is generally
made smaller for that purpose.
The nonmagnetic support functions not only to give a mechanical or
physical strength to the magnetic recording medium in the
longitudinal and width directions but also to absorb a shock caused
by a pressure applied to the recording medium in the depth
direction. That is, the nonmagnetic support absorbs a shock given
to the magnetic recording layer when the recording layer is brought
into contact with a magnetic head, whereby the recording layer is
prevented from suffering damages caused by the contact with a
magnetic head. For this reason, as the thickness of the nonmagnetic
support is made smaller, the function of shock absorption of the
nonmagnetic support decreases. Especially in recent days, it is
required for a thin nonmagnetic support to provide a high strength
to the magnetic recording medium, so that a resin film having high
mechanical or physical strength is widely employed. However, such
resin film is generally rigid, and hence the nonmagnetic support of
such resin film is liable to be decreased in the above-mentioned
function of shock absorption.
By the decrease of the function of shock absorption of the
nonmagnetic support, there arises a problem that a ferromagnetic
powder easily separates (drops off) from the magnetic recording
layer to deposit on a magnetic head when the recording layer is
brought into contact with the head, whereby running endurance of
the recording medium is deteriorated.
A magnetic recording medium having a recording layer in the form of
two layers has been already known, and the known magnetic recording
layer of two-layer type generally comprises a flexible (soft) upper
layer and a lower layer of high hardness. That is, in the magnetic
recording medium having such structure, the upper layer of the
magnetic recording layer which is to be in contact with a magnetic
head is made flexible, and thereby the magnetic recording layer can
be enhanced in easiness of close contact with the head.
However, it has been confirmed by the present inventors that the
above-mentioned magnetic recording medium having a two-layer type
magnetic recording layer including the upper flexible layer and the
lower layer of high hardness decreases in running property and
running endurance, and additionally the recording medium shows poor
bonding strength between the nonmagnetic support and the magnetic
recording layer. Also confirmed is that a magnetic tape having such
constitution of the magnetic recording layer shows an extreme
variation of electromagnetic conversion characteristics (i.e.,
variation of output level) when stored under condition of high
temperatures such as a temperature of higher than 60.degree. C. It
is presumed that the variation of electromagnetic conversion
characteristics in the storage at high temperatures takes place for
the following reason. When the magnetic tape is stored in the wound
state at a high temperature, the upper layer of the magnetic
recording layer is made more soft by the high temperature, and the
protruded and depressed portions of the surface of the nonmagnetic
support of the magnetic tape are copied onto the surface of the
upper layer of the magnetic recording layer. As a result,
electromagnetic conversion characteristics of the medium varies in
the reproduction procedure.
Japanese Patent Provisional Publication No. 57(1982)-78630
discloses a magnetic recording medium comprising two magnetic
recording layers in which the orientations of the ferromagnetic
powders contained in the two recording layers are made different
from each other, whereby the ratio of the elasticity modulus
between in the longitudinal direction and in the width direction of
the medium is in the specific range. The magnetic recording medium
is improved in strength particularly in the edge portion. However,
the recording medium is not improved as far as the electromagnetic
conversion characteristics, running property and running endurance
are concerned.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic
recording medium such as a magnetic tape which is improved in
electromagnetic conversion characteristics, running property and
running endurance.
More particularly, the object of the invention is to provide a
magnetic recording medium less suffering clogging on a magnetic
head and showing high running endurance.
There is provided by the present invention a magnetic recording
medium comprising a nonmagnetic support and a magnetic recording
layer provided on the support which comprises two layers including
a first magnetic recording layer and a second magnetic recording
layer, each of said first and second magnetic recording layers
comprising a binder and a ferromagnetic powder having a coercive
force of not less than 500 Oe dispersed therein, wherein:
said first magnetic recording layer provided on the nonmagnetic
support has a Young's modulus in the longitudinal direction of 500
to 1,000 kg/mm.sup.2 ;
said second magnetic recording layer provided on the first magnetic
recording layer has a Young's modulus of not less than 1,300
kg/mm.sup.2 ; and
the magnetic recording layers as a whole show a Young's modulus in
the longitudinal direction of not less than 900 kg/mm.sup.2.
In the magnetic recording medium of the present invention, the
first magnetic recording layer provided on the nonmagnetic support
effectively functions to absorb a shock caused by a pressure
applied to the recording layer because it is made highly flexible.
For example, the first magnetic recording layer absorbs a shock
given to the magnetic recording medium when the surface of magnetic
recording layer is brought into contact with a magnetic head, and
hence the occurrence of damages on the magnetic recording layer is
prominently reduced. Moreover, since the ferromagnetic powder
hardly separates (drops off) from the magnetic recording layer so
as not to deposit onto the magnetic head, the running endurance of
the recording medium is improved. Further, the second magnetic
recording layer, the surface of which is brought into contact with
a magnetic head, is made rigid, so that the recording layer hardly
suffers from abrasion or distortion (deformation) even when the
recording layer is in contact with the head, and the ferromagnetic
powder does not easily drop off from the recording layer.
In addition to the above-mentioned favorable features, the magnetic
recording medium of the invention is hardly deformed even when
stored in an atmosphere of high temperatures, and accordingly
copying of the protruded and depressed portions of the nonmagnetic
support onto the surface of the magnetic recording layer is
prominently reduced in the storage of the medium in the wound
state.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a sectional view showing a constitution of a magnetic
recording medium according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1 of the attached drawing, the magnetic recording
medium of the present invention basically comprises a nonmagnetic
support 11 and a magnetic recording layer 12 provided on the
surface of the support. The magnetic recording layer 12 consists of
the first magnetic recording layer 12a and the second magnetic
recording layer 12b, each having a specific Young's modulus which
is different from each other.
A conventional magnetic recording medium is generally prepared by a
method of providing a magnetic recording layer on the nonmagnetic
support in the form of sheet or film through a coating method, and
the magnetic recording medium of the invention can be also prepared
utilizing the known method.
For obtaining the specific Young's modulus of each of the first and
second magnetic recording layers defined in the invention, there
can be utilized various methods such as a method of using
substantially the same ferromagnetic powders for both layers (e.g.,
Co-containing .gamma.-iron oxide, but their surface area or
coercive force may be different from each other) in the same
amounts and using a binder of the first magnetic recording layer
which has a Young's modulus lower than that of the binder of the
second magnetic recording layer; a method of using the same binders
in both layers and using a ferromagnetic powder in the first
magnetic recording layer in an amount smaller than that in the
second magnetic recording layer; and a method of adjusting both of
the amounts of the ferromagnetic powders and the kinds of the
binders for the first and second magnetic recording layers so as to
determine the Young's moduli of those layers.
A process for the preparation of a magnetic recording medium of the
invention which is specified in the Young's moduli of the first and
second magnetic recording layers will be described hereinafter,
referring to the above-mentioned method using the same
ferromagnetic powders in the same amounts and using a binder of the
first magnetic recording layer which has a Young's modulus lower
than that of the binder of the second magnetic recording layer.
Examples of materials of the nonmagnetic support include polyester
resins, polyolefin resins, cellulose derivatives, polycarbonate
resins, polyamide resins, polyimide resins and polyamideimide
resins. There can be also employed other materials depending on the
purpose such as films of nonmagnetic metals (e.g., aluminum,
copper, tin, zinc and a nonmagnetic metal containing thereof),
plastic films deposited with a metal such as aluminum, and various
papers (e.g., an ordinary paper and papers coated or laminated with
polyolefins).
There is no specific limitation on the shape of the nonmagnetic
support, and any shape (form) such as sheet, film, tape, disc, card
and drum can be employed. Generally employed is a nommagnetic
support in the form of a sheet.
In the case of using a nonmagnetic support in the form of a sheet,
the thickness of the support is generally in the range of 5 to 50
.mu.m.
The nonmagnetic support may have a back layer (or backing layer) on
the opposite side of the side where a magnetic recording layer is
to be coated.
On the nonmagnetic support, a magnetic recording layer is provided.
The magnetic recording layer comprises a ferromagnetic powder
having a coercive force of not less than 500 Oe dispersed in a
binder.
As the ferromagnetic powder having a coercive force of not less
than 500 Oe, there can be mentioned a ferromagnetic powder of
Co-containing iron oxide, a ferromagnetic powder of chromium
dioxide, a ferromagnetic metal powder and barium ferrite.
The ferromagnetic powder generally used is in a needle shape, and
the needle ratio thereof is preferably in the range of 2/1 to 20/1,
more preferably in the range of 5/1 to 20/1. The average length of
the ferromagnetic powder is in the range of 0.2 to 2.0 .mu.m. The
shape of the ferromagnetic powder is by no means restricted to the
needle shape, and any other shapes conventionally used such as rice
shape or plate shape can be also employed in the invention.
In the invention, it is particularly preferred to use a
ferromagnetic powder having a coercive force of not less than 500
Oe and having a specific surface area of not less than 42 m.sup.2
/g (preferably not less than 50 m.sup.2 /g).
In the case of using a ferromagnetic metal powder, preferred is a
ferromagnetic alloy powder containing a metal component in which at
least 75 wt.% (preferably at least 80 wt.%) of the metal component
comprises at least one ferromagnetic metal or metal alloy (e.g.,
Fe, Co, Ni, Fe-Co, Fe-Ni, Co-Ni or Fe-Co-Ni) and having a
longitudinal diameter of not more than 1.0 .mu.m.
As the binder employable for the magnetic recording layer according
to the invention, there can be mentioned those conventionally used
for the formation of a magnetic recording layer such as
thermoplastic resins, thermosetting resins and reaction curing
resins.
Examples of the thermoplastic resins include vinyl chloride/vinyl
acetate/maleic anhydride copolymer resins, vinyl chloride/vinyl
acetate copolymer resins, cellulose derivatives, vinylidene
chloride resins, polyester resins, (meth)acrylic resins, polyvinyl
acetal resins, polyvinyl butyral resins, butadiene/acrylonitrile
copolymer resins, polyamide resins, polyvinyl fluoride resins and
nylon/silicone resins. The thermoplastic resin employable in the
invention has a softening temperature of not higher than
150.degree. C. and an average molecular weight of 10,000 to
200,000.
Examples of the thermosetting resins and reaction curing resins
include polyurethane resins, urea resins, melamine resins, phenoxy
resins, epoxy resins, urethane epoxy resins, a mixture of polyester
polyol and polyisocyanate, urea/formaldehyde resins, polyamide
resins and a mixture of low molecular glycol, high molecular diol
and triphenylmethane triisocyanate. The thermosetting resin or
reaction curing resin employable in the invention has a molecular
weight of not more than 200,000 before it is cured and a molecular
weight of almost infinity after curing reaction.
The above-mentioned resins can be employed independently or in
combination as the binder.
The binder used in the first magnetic recording layer is selected
from those having a Young's modulus lower than that of the binder
used for the second magnetic recording layer.
As the binder of the second magnetic recording layer, a combination
of a vinyl chloride/vinyl acetate/maleic anhydride copolymer and a
polyurethane resin is particularly preferred. In this case (i.e.,
the case of using such combination), a polyisocyanate compound is
preferably used as a curing agent together with the combination,
whereby the resulting second magnetic recording layer is enhanced
in hardness, and hence the surface of the magnetic recording layer
can be prevented from separation or dropping of the ferromagnetic
powder which is caused by the contact between the surface of the
magnetic recording layer and a magnetic head. As a result, the
resulting recording medium is further improved in running
endurance.
When the above-mentioned vinyl chloride/vinyl acetate/maleic
anhydride copolymer, polyurethane resin and polyisocyanate compound
are employed in combination as the binder of the second magnetic
recording layer, the ratio between the vinyl chloride/vinyl
acetate/maleic anhydride copolymer and the polyurethane resin is
preferably in the range of 1:0.1 to 1:1 (vinyl chloride/vinyl
acetate/maleic anhydride copolymer:polyurethane resin, by weight),
and the ratio between the polyurethane resin and the polyisocyanate
compound is preferably in the range of 1:1 to 1:3 (polyurethane
resin:polyisocyanate compound, by weight). The amount of the
polyurethane resin contained in the binder of the second magnetic
recording layer is preferably smaller than 50 wt.%, more preferably
not larger than 30 wt.%. In the case of not larger than 30 wt.%,
the Young's modulus of the second magnetic recording layer
increases, and thereby occurrence of separation or dropping of the
ferromagnetic powder from the surface of the second magnetic
recording layer can be much more reduced even when the surface of
the magnetic recording layer is brought into contact with a
magnetic head.
As the binder of the first magnetic recording layer, there can be
mentioned resin components (including resin composition) inherently
having a low Young's modulus among the aforementioned resin
components. Examples of the binder of the first magnetic recording
layer include a polyurethane resin and a saturated polyester resin.
They can be employed singly or in combination. In the case of using
the polyurethane resin, a small amount of a polyisocyanate compound
can be used in combination as a curing agent.
When the polyurethane resin is used as a binder component of the
first magnetic recording layer, the binder of the first magnetic
recording layer preferably contains the polyurethane resin in an
amount of not smaller than 50 wt.%, more preferably not smaller
than 60 wt.%. The polyurethane resin is inherently soft, so that
especially when the polyurethane resin is used in an amount of not
smaller than 60 wt.%, the Young's modulus of the first magnetic
recording layer decreases, whereby the first magnetic recording
layer favorably functions to effectively absorb a shock.
The amount of the binder contained in each of the first and second
magnetic recording layers is generally in the range of 15 to 45
parts by weight based on 100 parts by weight of the ferromagnetic
powder contained in each layer.
Both of the first and second magnetic recording layers may contain
other additives conventionally used such as a lubricant, an
abrasive, a dispersing agent, an antistatic agent and a corrosion
inhibitor. Examples of the lubricant employable in the invention
include saturated or unsaturated higher fatty acid, fatty acid
ester, higher fatty acid amide, higher alcohol, silicon oil,
mineral oil, vegetable oil, fluorine compound, and a solid
lubricant such as graphite.
The magnetic recording medium of the present invention can be
prepared, for example, by the following process.
In the first place, a magnetic paint for the formation of the first
magnetic recording layer (referred to hereinafter as "first
magnetic paint") and a magnetic paint for the formation of the
second magnetic recording layer (referred to hereinafter as "second
magnetic paint") are prepared by a known method using the
components for the formation of those magnetic recording layers
containing a ferromagnetic powder having a coercive force of not
less than 500 Oe and a binder as the host components. The
components for the formation of those magnetic recording layers may
also contain other additives such as a lubricant, an abrasive, a
dispersing agent, an antistatic agent and a corrosion inhibitor, if
desired. In the preparation of the first and second magnetic
paints, the same kind of ferromagnetic powders are used in the same
amounts for those magnetic paints, and as the binder of the first
magnetic paint, a binder having a Young's modulus lower than that
of the binder of the second magnetic paint is employed.
In the second place, the first and second magnetic paints prepared
as above are coated in such a manner that the first magnetic paint
and the second magnetic paint are arranged on the nonmagnetic
support in this order, so as to form a magnetic recording layer
comprising the first and second magnetic layers on the support.
Thus, a magnetic recording medium of the present invention can be
prepared.
In the coating procedure, the first magnetic paint having a
relatively lower Young's modulus is coated on the nonmagnetic
support, and then the second magnetic paint having a relatively
higher Young's modulus is coated on the coated layer of the first
magnetic paint.
The coating procedure can be carried out by coating the first
magnetic paint on the nonmagnetic support and then coating the
second magnetic paint on the coated layer of the first magnetic
paint. Otherwise, it is also possible to simultaneously apply those
first and second magnetic paints on the nonmagnetic support in the
superposed form by the use of a simultaneous superposition coating
machine.
The coating procedure is performed in such a manner that whole
thickness of the resulting magnetic recording layer of the magnetic
recording medium would be in the range of 2.0 to 10 .mu.m.
Accordingly, in the case of utilizing a simultaneous superposition
coating, each layer of the first and second magnetic paints is
generally determined based on half thickness of the above-defined
thickness. For the purpose of preventing the aforementioned
transferring in the long-term storage of a magnetic recording
medium, it is desired that the thickness of the second magnetic
recording layer is not larger than 2 .mu.m and the thickness of the
first magnetic recording layer is larger than that of the second
magnetic recording layer.
The coated layers of the magnetic paints are generally subjected a
magnetic orientation under wet condition so as to orient the
ferromagnetic powder contained in the magnetic recording layer.
Then, the coated layers of the magnetic paints are subjected to a
drying process to give a magnetic recording layer. The drying
process is generally carried out by heating the coated layers at a
temperature of 50.degree. to 120.degree. C. for 10 second to 5
minutes.
After the coated is dried, the surface of the magnetic recording
layer is subjected to a surface smoothening process, and then the
resulting sheet comprising a magnetic recording layer and a
nonmagnetic support is cut or slit into a desired shape.
Thus, there can be prepared a magnetic recording medium of the
invention in which a Young's modulus of the first magnetic
recording layer is 500 to 1,000 kg/mm.sup.2, a Young's modulus of
the second magnetic recording layer provided on the first magnetic
recording layer is not less than 1,300 kg/mm.sup.2, and a Young's
modulus of the whole of the magnetic recording layer is not less
than 900 kg/mm.sup.2.
In the case of forming each of the first and second magnetic
recording layers by adjusting the amounts of the ferromagnetic
powders for those layers, a process according to the
above-described one can be utilized.
The examples and the comparison examples of the present invention
are given below. In the following examples, the term "part(s)"
means "part(s) by weight", unless otherwise specified.
PREPARATION OF MAGNETIC PAINT
A ferromagnetic powder, binder components (excluding a
polyisocyanate compound), additives and a solvent set forth in each
of the following three kinds of compositions (Composition X, Y and
Z) for magnetic paints were well kneaded in a ball mill to give a
mixture. To the mixture was added a polyisocyanate compound
indicated in the following binder components and they were
sufficiently kneaded to prepare three kinds of magnetic paints. The
amounts of the binder components used in the preparation of a
magnetic paint are set forth in each example.
Composition X
Ferromagnetic Powder
Co-containing .gamma.-FeO.sub.x (x=1.45, Hc: 650 Oe, specific
surface area: 30 m.sup.2 /g) 100 parts
Binder Components
Vinyl chloride/vinyl acetate/vinyl alcohol copolymer
(copolymerization ratio=92:2:6, degree of polymerization: 400)
Polyester polyurethane resin (molecular weight: 50,000)
Polyisocyanate compound (Desmodule L-75, available from Bayer
AG)
Additives
Myristic acid: 2 parts
Oleic acid modified silicon: 2 parts
Solvent
Methyl ethyl ketone: 300 parts
Composition Y
Ferromagnetic Powder
Co-containing .gamma.-FeO.sub.x (x=1.45, Hc: 650 Oe, specific
surface area: 40 m.sup.2 /g): 100 parts
Binder Components
Vinyl chloride/vinyl acetate/vinyl alcohol copolymer
(copolymerization ratio=92:2:6, degree of polymerization: 400)
Polyester polyurethane resin (molecular weight: 50,000)
Additives
Myristic acid: 2 parts
Oleic acid modified silicon: 2 parts
.alpha.-Alumina: 0.5 part
Conductive carbon: 0.5 part
Solvent
Methyl ethyl ketone 300 parts
Composition Z
Ferromagnetic Powder
Co-containing .gamma.-FeO.sub.x (x=1.45, Hc: 650 Oe, specific
surface area: 50 m.sup.2 /g): 100 parts
Binder Components
Vinyl chloride/vinyl acetate/vinyl alcohol copolymer
(copolymerization ratio=92:2:6, degree of polymerization: 400)
Polyester polyurethane resin (molecular weight: 50,000)
Polyisocyanate compound
(Desmodule L-75, available from Bayer AG)
Additives
Stearic acid: 1 part
Butyl stearate: 7 parts
.alpha.-Alumina: 2 parts
Conductive carbon: 2 parts
Solvent
Methyl ethyl ketone: 300 parts
EXAMPLE 1
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 9 parts, 15 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer and the polyester polyurethane
resin in Composition Y were set to 27 parts and 3 parts,
respectively, to prepare a magnetic paint (i.e., second magnetic
paint) according to the above-mentioned procedure.
The first and second magnetic paints obtained as above were
simultaneously coated over a polyethylene terephthalate support of
10 .mu.m thick in the superposed form, to give a coated layer of
the first magnetic paint having thickness of 4 .mu.m (in dry basis)
on the support and a coated layer of the second magnetic paint
having thickness of 1 .mu.m (in dry basis) on the coated layer of
the first magnetic paint. The support with the coated layers was
subjected to a magnetic orientation while the coated layers were
wet, and then heated at a temperature of 100.degree. C. for one
minute to remove the solvent.
After the drying, the resulting sheet was subjected to a surface
smoothening treatment by means of a calender roll and further
subjected to another heat treatment. The sheet was then slit to
give an audio compact cassette tape (audio tape) having a width of
3.8 mm.
EXAMPLE 2
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 9 parts, 15 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer and the polyester polyurethane
resin in Composition Y were set to 24 parts and 6 parts,
respectively, to prepare a magnetic paint (i.e., second magnetic
paint) according to the above-mentioned
Using the obtained first and second magnetic paints, an audio
compact cassette tape was prepared in the same manner as described
in Example 1.
EXAMPLE 3
The procedure of Example 1 was repeated except for varying the
thickness of the coated layers of the second magnetic paint and the
first magnetic paint to 2 .mu.m and 3 .mu.m (both in dry basis),
respectively, to prepare an audio compact cassette tape.
EXAMPLE 4
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 9 parts, 15 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer and the polyester polyurethane
resin in Composition Y were set to 30 parts and O part,
respectively, to prepare a magnetic paint (i.e., second magnetic
paint) according to the above-mentioned procedure.
Using the obtained first and second magnetic paints, an audio
compact cassette tape was prepared in the same manner as described
in Example 1.
COMPARISON EXAMPLE 1
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 9 parts, 15 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer and the polyester polyurethane
resin in Composition Y were set to 21 parts and 9 parts,
respectively, to prepare a magnetic paint (i.e., second magnetic
paint) according to the above-mentioned procedure.
Using the obtained first and second magnetic paints, an audio
compact cassette tape was prepared in the same manner as described
in Example 1.
COMPARISON EXAMPLE 2
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 15 parts, 9 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer and the polyester polyurethane
resin in Composition Y were set to 27 parts and 3 parts,
respectively, to prepare a magnetic paint (i.e., second magnetic
paint) according to the above-mentioned procedure.
Using the obtained first and second magnetic paints, an audio
compact cassette tape was prepared in the same manner as described
in Example 1.
The audio compact cassette tapes prepared in Examples 1 to 4 and
Comparison Examples 1 and 2 were measured on Young's moduli of an
upper layer of the magnetic recording layer (i.e., first magnetic
recording layer), a lower layer of the magnetic recording layer
(i.e., second magnetic recording layer) and the whole of the
magnetic recording layer by means of a viscoelasticity spectrometer
(produced by Toyo Baldwin Co., Ltd.). The results are set forth in
Table 1.
The audio tapes were further evaluated on variation of output
level, running property, tape squeak, and easiness in close contact
with a magnetic head (i.e., contact property) according to the
following tests. The results are also set forth in Table 1.
Variation of output level
The audio tape was recorded with a signal of 10 KHz and -10 dB. The
tape was then wound over a hub and kept in an atmosphere of
80.degree. C. for 24 hours. The tape was taken out of the
atmosphere and placed under ambient conditions for one hour. The
signal was then reproduced for determining variation of the output
level.
The results of the evaluation are classified into the
following:
A: variation of output level of not more than 1 dB;
B: variation of output level of more than 1 dB to not more than 3
dB;
C: variation of output level of more than 3 dB to not more than 6
dB; and
D: variation of output level of more than 6 dB.
Running property
100 audio tapes (for each example) were allowed to stand in an
atmosphere of 80.degree. C. for 24 hours, and then taken out of the
atmosphere and placed under ambient conditions for one hour. The
audio tapes were repeatedly run in 100 commercially available tape
recorders at 20 times of round-trip, to count the number of tapes
in which tape-running stop took place.
The results of the evaluation are classified into the
following:
A: tape-running stop does not take place on any tape;
B: tape-running stop takes place on one tape;
C: tape-running stop takes place on two tapes; and
D: tape running stop takes place on three or more tapes.
Tape squeak
In the above-mentioned test for evaluating the running property,
the number of tapes in which tape squeak took place was
counted.
The results of the evaluation are classified into the
following:
A: tape squeak does not take place on any tape;
B: tape squeak takes place on one tape;
C: tape squeak takes place on two tapes; and
D: tape squeak takes place on three or more tapes.
Contact property
The contact property of the audio tape with a magnetic head was
evaluated by examining a bonding strength between the magnetic
recording layer and the nonmagnetic support according to a T-peel
test. The evaluation was made by measuring a tension required for
peeling (separating) the magnetic recording layer from the
support.
The results of the evaluation are classified into the
following:
A: tension of not less than 50 g.;
B: tension of 35 to 45 g.;
C: tension of 20 to 34 g.; and
D: tension of not more than 19 g.
TABLE 1 ______________________________________ Example Com. Example
1 2 3 4 1 2 ______________________________________ Young's modulus
(Oe) Upper layer 1,700 1,400 1,700 1,900 1,000 1,700 Lower layer
800 800 800 800 800 1,100 Whole layer 980 920 1,160 1,020 840 1,220
Variation of output level A A A A C A Running property A A A A B B
Tape squeak A A A A B A Contact property A A B A A C
______________________________________
EXAMPLE 5
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane and the polyisocyanate in
Composition X were set to 9 parts, 15 parts and 6 parts,
respectively, to prepare a magnetic paint (i.e., first magnetic
paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer, polyester polyurethane resin and
the polyisocyanate compound in Composition Z were set to 12 parts,
7.5 parts and 10.5 parts, respectively, to prepare a magnetic paint
(i.e., second magnetic paint) according to the above-mentioned
procedure.
The first and second magnetic paints obtained as above were
simultaneously coated over a polyethylene terephthalate support of
10 .mu.m thick in the superposed form, to give a coated layer of
the first magnetic paint having thickness of 4 .mu.m (on dry basis)
on the support and a coated layer of the second magnetic paint
having thickness of 1 .mu.m (in dry basis) on the coated layer of
the first magnetic paint. The support with the coated layers was
subjected to a magnetic orientation while the coated layers were
wet, and then heated at a temperature of 100.degree. C. for one
minute to remove the solvent.
After the coated layer was dried, the resulting sheet was subjected
to a surface smoothening treatment by means of a calender roll and
further subjected to another heat treatment. The sheet was then
slit to give a VHS type video cassette tape (video tape) having a
width of 1/2 inch.
COMPARISON EXAMPLE 3
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polyurethane resin and the polyisocyanate
compound in Composition X were set to 9 parts, 15 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer, polyester polyurethane resin and
the polyisocyanate compound in Composition Z were set to 9 parts,
15 parts and 6 parts, respectively, to prepare a magnetic paint
(i.e., second magnetic paint) according to the above-mentioned
procedure.
Using the obtained first and second magnetic paints, a VHS type
video cassette tape was prepared in the same manner as described in
Example 5.
COMPARISON EXAMPLE 4
The amounts of the vinyl chloride/vinyl acetate/vinyl alcohol
copolymer, polyester polurethane resin and the polyisocyanate
compound in Composition X were set to 15 parts, 9 parts and 6
parts, respectively, to prepare a magnetic paint (i.e., first
magnetic paint) according to the above-mentioned procedure.
Independently, the amounts of the vinyl chloride/vinyl
acetate/vinyl alcohol copolymer, polyester polyurethane resin and
the polyisocyanate compound in Composition Z were set to 12 parts,
7.5 parts and 10.5 parts, respectively, to prepare a magnetic paint
(i.e., second magnetic paint) according to the aforementioned
procedure.
Using the obtained first and second magnetic paints, a VHS type
video cassette tape was prepared in the same manner as described in
Example 5.
The video cassette tapes prepared in Example 5 and Comparison
Examples 3 and 4 were measured on Young's moduli of an upper layer
of the magnetic recording layer (i.e., first magnetic recording
layer), a lower layer of the magnetic recording layer (i.e., second
magnetic recording layer) and the whole of the magnetic recording
layer by means of a viscoelasticity spectrometer (produced by Toyo
Baldwin Co., Ltd.). The results are set forth in Table 2.
The video tapes were further evaluated on still life and easiness
in close contact with a magnetic head (i.e., contact property)
according to the following tests. The results are also set forth in
Table 2.
Still life
The video tape was run in a commercially available VHS type video
tape recorder under a still mode to determine a term (i.e., still
life) at the end of which the video output decreased by 6 dB. The
results of the evaluation are classified into the following:
A: still life of not shorter than 120 minutes;
B: still life of not shorter than 60 minutes and shorter than 120
minutes;
C: still life of not shorter than 30 minutes and shorter than 60
minutes; and
D: still life of shorter than 30 minutes.
Contact property
The contact property of the video tape with a magnetic head was
evaluated by examining a bonding strength between the magnetic
recording layer and the nonmagnetic support according to a T-peel
test. The evaluation was made by measuring a tension required for
peeling (separating) the magnetic recording layer from the
support.
The results of the evaluation are classified into the
following:
A: tension of not less than 50 g.;
B: tension of 35 to 45 g.;
C: tension of 20 to 34 g.; and
D: tension of not more than 19 g.
TABLE 2 ______________________________________ Young's Modulus (Oe)
Upper Lower Whole Still Contact layer layer layer Life Property
______________________________________ Example 5 1,500 800 940 A A
Com. Ex. 3 800 800 800 C A Com. Ex. 4 1,500 1,100 1,180 A C
______________________________________
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